PHILADELPHIA – Art Gutierrez comes to the corner of Kensington Avenue and Somerset Street every morning to buy heroin.

What he's actually getting in Philadelphia's notorious open-air drug market is heroin laced with an even more potent additive, often in unpredictable amounts that even antidotes can't stop from being deadly. That narcotic, increasingly spliced into the nation's illicit drug supply, is fentanyl, a synthetic painkiller exacerbating heroin's deadly trap. In cities across America, it is fueling deeper addiction and has become one of the most prominent killers linked to the nation's drug crisis.

"It's a new epidemic," said Gutierrez, 42, who shoots up on the sidewalks here in Kensington by day and ducks into abandoned buildings to sleep at night as he copes with crippling addiction. He has watched his friends die and says, "If you catch a pure bag of fentanyl, that Narcan ain't bringing you back."

This city, like many others across the United States long mired in a battle against opioid addiction, is seeing the precipitous rise of illicit fentanyl. Once a minor player in the drug crisis, the man-made narcotic – about 50 times stronger than heroin – is directly linked to thousands of overdoses and a shocking rise in fatalities nationwide, a trend that is particularly noticeable in the nation's urban areas.

In 24 of the nation's largest cities and the counties that surround them, fentanyl-related overdose deaths increased nearly 600 percent from 2014 to 2016, according to county health departments nationwide. According to overdose records in those cities reviewed by The Washington Post, there were 582 fatal overdoses linked to fentanyl in 2014, a number that soared to 3,946last year. Officials estimate there will be a much higher number of fatal fentanyl-related overdoses in 2017.

Cook County, Illinois, (Chicago) recorded a 2,700 percent increase in fatal fentanyl-related overdoses, jumping from 20 in 2014 to 562 in 2016. Orange County, Florida, (Orlando) saw its 34 fatal fentanyl overdoses in 2014 triple to 105 in 2016. And Franklin County, Ohio, (Columbus) went from 13 such overdoses two years ago to 111 in 2016.

Law enforcement and public health officials say they are alarmed by the rate at which fentanyl has infiltrated the illicit drug market and how it is transforming the face of the drug crisis, which resulted in 60,000 fatal overdoses in 2016, more than half of which were from opioids.

"If anything can be likened to a weapon of mass destruction in what it can do to a community, it's fentanyl," said Michael Ferguson, the special agent in charge of the Drug Enforcement Administration's New England division. "It's manufactured death."

The spike in fatal fentanyl overdoses in greater Philadelphia has been among the steepest. In 2012, the drug was linked to nine fatal overdoses, according to the health department. By 2014, that number had grown to 100 fentanyl-linked overdoses. Pennsylvania law enforcement officials just announced last year's totals: Fentanyl was responsible for more than 400 overdose deaths in Philadelphia last year and more than 2,000 fatal overdoses statewide – marking the first time in recent state history that heroin was not the most deadly overdose drug.

"The trend is not going to change, unfortunately," said Patrick Trainor, a DEA special agent in Philadelphia. "Not anytime soon."

Philadelphia's Health Commissioner Thomas Farley said the city is averaging 100 overdose deaths per month in 2017, noting that fentanyl "has thrown gasoline onto a fire that was already raging."

"This is a health crisis that's worse than we've ever seen," Farley said. "This will kill more people than the AIDS epidemic. You'd have to go back to the influenza pandemic of 1918 if you even wanted to start making comparisons."

Officials note that in some places medical examiners did not test overdose victims for fentanyl – which does not show up on all standard drug screenings – until 2015, probably causing an undercount in its lethality until then. But they say the raw number of fentanyl-related deaths last year was staggering.

President Donald Trump on Thursday agreed, saying that the opioid crisis is a national emergency, pledging more money and attention to the problem.

"It is a serious problem, the likes of which we've never had. You know, when I was growing up, they had the LSD, and they had certain generations of drugs," Trump said. "There's never been anything like what's happened to this country over the last four or five years."

Trash left by drug users under a bridge near train tracks in Philadelphia. (Washington Post photo by Salwan Georges)

The U.S. opioid epidemic can be traced to the 1990s, when the pharmaceutical industry began producing new opioid painkillers, such as OxyContin, that were marketed as safer and less prone to abuse than prior medications. At the same time, the medical establishment seized on the notion that freedom from pain is a human right and a "vital sign," much like blood pressure or heart rate.

Suddenly, opioid painkillers were prescribed for a wide range of ailments. In some communities already ravaged by joblessness and substance abuse, unscrupulous doctors dispensed the painkillers in bulk via "pill mills." As officials sought to reduce illegitimate prescriptions, the street price of the painkillers soared, sending many users to relatively cheaper heroin, mostly imported from Mexico.

As users developed tolerances for the heroin, dealers in search of something cheaper and even stronger began mixing in illicit fentanyl – a synthetic drug that in its legal form is sometimes used in anesthesia to prevent surgical pain. Soon, even as overdoses spiked, countless drug abusers sought out the more powerful fentanyl-laced heroin, and thousands of users became hooked on the more potent drug.

Amanda Bennett, 26, of Baltimore became addicted to opioids after she was prescribed oxycodone while recovering from an emergency C-section. Her addiction transitioned from pills to heroin, which then escalated to fentanyl-laced heroin.

"If there's no fentanyl in it, I don't want it at all. I'm addicted to the fentanyl. If there's no fentanyl in it, it doesn't get me well at all," Bennett said, using a phrase common to heroin users for how the drugs make them feel.

Bennett, whose two children, ages 7 and 4, live with their godmother, said she tried a 14-day rehab stay, but the pull of the drug was too strong. The first thing she did after getting out was get high.

"I made 'em bring me some. . . . I wasn't ready," she said. "This is all I know anymore. It's all I know."

Miami's fentanyl problem came into stark view in July, when authorities released preliminary toxicology results showing that 10-year-old Alton Banks died in June from a combination of heroin and fentanyl. The state attorney there raised the possibility that Alton came into contact with the drugs at a community pool or on his walk home through a neighborhood known to be an illicit drug marketplace. Because contact with fentanyl could be deadly, some police departmentssend doctors with police on raids so they can treat officers who encounter drugs. An officer in East Liverpool, Ohio, said he accidentally overdosed in May after a traffic stop when he used his hand to brush powdered fentanyl off his uniform.

While many of those overdosing on fentanyl specifically aimed to use the drug, health providers and police officials say many overdoses occur among users who did not know the powerful opioid had been cut into heroin – or even their cocaine.

Amber Snyder, 29, recalls a change in her father's behavior during the last months of his life. Ray Snyder's speech was slow and slurred, he wanted to sleep all day, his memory was shaky. Her father had been a substance abuser for as long as she could remember: alcohol, crack cocaine, heroin. But something this time was different.

The last night she saw him, she and her parents had ordered takeout from a Chicago Mediterranean restaurant, their Friday tradition. After dinner, Ray Snyder retreated to the basement, where he would often go to use drugs. He was found dead several hours later.

An autopsy report from the Cook County medical examiner's office revealed the truth to her: Ray Snyder, 46, died on Jan. 17, 2016, with cocaine and possibly heroin in his system. Also present: fentanyl.

"I expected to see cocaine. I expected perhaps to see heroin," she said. "But I did not expect, at all, to see fentanyl."

A hospital in New Haven, Connecticut, treated 12 overdoses, three of them fatal, in just an eight-hour period in June 2016 among people who thought they were using cocaine they purchased on the city's streets. The white powder turned out to be fentanyl. Overdose records in Philadelphia show that at least 162 people died there last year from a combination of fentanyl and cocaine, one such death almost every other day. In New York, which recorded more than 600 fentanyl-related fatal overdoses last year, at least 115 of the deaths were due to cocaine and fentanyl combinations.

Authorities and experts believe the migration of fentanyl into other drug supplies portends major problems. Daniel Raymond, policy director for the Harm Reduction Coalition, said the fact that fentanyl is showing up in cocaine in New York means it almost certainly will be in suburban and rural areas, too.

"Fentanyl ending up in a lot of the cocaine supply and reaching relatively naive users would be a super dangerous thing," Raymond said.

The illicit fentanyl often is imported directly from Chinese sources by mail or comes from Mexico, where the synthetic drug is manufactured using chemical compounds, experts and authorities said. Dealers then mix the powder into other drugs, making for imprecise potency in sometimes-lethal doses.

In Cleveland's Cuyahoga County, the medical examiner has raised concerns about overdose trends, blaming fentanyl-laced cocaine with spurring a doubling of African American fentanyl deaths in the county last year. Cocaine users often aren't aware they could encounter a dangerous opioid when they use.

Records show there were 10 fatal overdoses in Cleveland that included a combination of cocaine and fentanyl in 2014. Two years later, there were 141.

"You'd have to have been living under a rock to be using heroin and not know it might be tainted with fentanyl," said Joseph Pinjuh, an assistant U.S. attorney in Cleveland, where he has run the office's organized crime and drug enforcement task force since 1998. "The average cocaine user is totally unprepared for this."

People gather outside the Last Stop, a Narcotics Anonymous and Alcoholics Anonymous group at Kensington Avenue and Somerset Street – the heart of drug use and sales in Philadelphia. (Washington Post photo by Salwan Georges)

Tyrone Tavasci kicked his 18-year-old daughter Emma out of his Orange County, Calif., home after finding out that she was using drugs, sending the teen to live with her boyfriend.

"I just said I was scared for her and didn't want to see her going down the same path I went down," said Tavasci, 45, who works in recovery services after his own battle with substance use. Just a month later his daughter was begging him for help, and he got her into a rehabilitation center.

It didn't work. Six months later, on July 22, 2016, Emma was pronounced dead, her autopsy citing a cocktail of substances including cocaine, chemical traces of marijuana, two prescription drugs and fentanyl.

"She was aware of the risk of opiates," he said. "She very much had an 'I'm indestructible' point of view, and when it comes to that stuff, it doesn't discriminate."

In Philadelphia, there are an estimated 70,000 heroin users, according to a mayoral task force working to combat the opioid epidemic. As fentanyl kills more drug users, the number of people seeking training on how to use naloxone, an overdose-reversing drug sold under the name Narcan, has increased, according to Elvis Rosado, who facilitates trainings in Kensington. Many want to use Narcan as a lifeline, knowing they might need it when they get high.

"You get individuals who come in, and the first thing they say is 'I want to be trained for Narcan,' " Rosado said. "And they will go and say to their friends before they use, 'If anything happens I have Narcan in my pocket. Don't let me die.' "

Art Gutierrez, 42, left, sits at a storefront in July, as another man sleeps on the sidewalk in the Kensington neighborhood of Philadelphia. Fentanyl has been creeping into the heroin supply there, leading to a rise in overdoses. (Washington Post photo by Salwan Georges)

Most days, in the early mornings, Gutierrez gets his first hit of heroin free. Heroin has been sold in Kensington for decades, and the neighborhood, known colloquially as the Badlands, has a reputation for offering the purest kind. The introduction of fentanyl has led to increased competition, and dealers now aim for the best price and the highest potency.

Some give away a little product as an enticement, but the samples come with a deadly catch, Gutierrez said. One bag out of the batch usually contains a lethal dose of fentanyl. If word of an overdose from the lethal bag spreads, drug users seek out the dealer – because they know that dealer has the strongest product, the best fix for the money.

Gutierrez said his friend overdosed and died in an abandoned building earlier this year from a lethal sample.

"They hit him with a hotshot," he said. "The boy died instantly. He took his last breath sliding down the wall."

Gutierrez returns here because he has to. The pain of withdrawal is unbearable.

"Every bone in your body hurts," he said. "You get hot and cold sweats. It is 90 degrees out here but you'd be freezing with goose bumps. There is no middle ground."

But as people die around him, he wonders why he survives.

"Some of the best kids come out here and do one bag and die. They don't deserve it," he said. "Why am I still alive?"

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Achenbach reported from Boston and Baltimore. Kevin Sullivan in Miami contributed to this report.